Today's integrated circuits include a vast number of devices. Smaller devices and shrinking ground rules are the key to enhance performance and to reduce cost. As FET (Field-Effect-Transistor) devices are being scaled down, the technology becomes more complex, and changes in device structures and new materials are needed for maintaining the expected device performance improvements.
Germanium (Ge) is a strong candidate as a material to replace Si for advanced FET devices. It has significantly higher hole and electron mobilities than Si. Fabricating a Ge NFET, however, is challenging because of the low attainable n-type carrier concentration in the source and drain.